Denture alloy



United States Patent 3,544,315 DENTURE ALLOY Kama] Asgar, Ann Arbor,Mich., assignor to The Regents of The University of Michigan, Ann Arbor,Mich. No Drawing. Filed Mar. 12, 1969, Ser. No. 806,669 Int. Cl. C22c19/00 US. Cl. 75171 3 Claims ABSTRACT OF THE DISCLOSURE An alloy fordental appliances containing as essential ingredients 50% to 60% cobalt,20% to 28% chromium, to 20% nickel, 3.7% to 4.1% molybdenum and 0.18% to0.22% carbon has high strength and improved elongation and toughness.

This invention pertains to an alloy having high strength and improvedelongation and toughness that is particularly adapted for the productionof cast dentures. More. particularly, this invention concerns an alloyhaving as its principal constituents cobalt, chromium and nickel, andcontaining minor but critical amounts of molybdenum and carbon.

Cobalt-chromium alloys are widely used in the production of castings fordenture appliances, either partial or complete. Dentists, dentaltechnicians and patients have been dissatisfied with the performance ofthe available alloys because of certain inadequate physical properties.More specifically, due to the low elongation, inadequate toughness, andhigh hardness of the known chrome-cobalt alloys, minor but necessaryadjustments required at the time of delivery to the patient arediflicult and consume valuable chair time. The technician or dentistmust be extremely cautious to avoid bending a clasp attachment throughmore than about a five to ten degree angle or breakage occurs. Moreover,the available alloys lack of toughness is dramatically demonstrated byready breakage of the dentures when accidentally dropped on the floor bythe dentist or patient. Their inadequate toughness is also manifested,perhaps less dramatically, by the early breakage of the denture claspsdue to stresses of ordinary use by the wearer. The problem is compoundedby the fact that the clasp must have sufficient rigidity to retain theshape and position to which it has been adjusted and not be altered bythe biting forces. The extreme hardness of the known alloys also is aserious problem because of the wear the denture causes to opposing teethin contact therewith. Moreover, high hardness prevents slightadjustments of the clasp by grinding (occlusion).

The cobalt-chromium alloy of this invention alleviates the foregoingdifliculties because of improved properties flowing from an unexpectedcritical combination of narrowly defined molybdenum and carbon contents.

In accordance with this invention, an alloy is provided containing asessential ingredients at least 50 and up to 60 but preferably up to 55percent cobalt, 20 to 28 percent chromium, 10 to 20 percent nickel, 3.7to 4.1 percent molybdenum and 0.18 to 0.22 percent carbon, said alloyhaving an elongation of at least ten percent and a tough ness factor ofat least 9000. The yield point of the alloy is greater than 50,000p.s.i. and its hardness is not greater than about 310 DPH.

The percentage of elongation is a measure of the amount an alloy willincrease in length as it is drawn from a zero to the breaking point.Percentage of elongation has a direct relationship to cold shaping of analloy as in the use of pliers to shape wire into clasps. The yield pointis an indication of the behavior of a clasp as well as the entiredenture frame under biting forces, which forces can easily producestresses above the yield strength of an alloy deficient in that propertycausing the denture to shift out of proper occlusal' relationship towhich it was originally designed. Toughness is the ability of an alloyto Withstand sudden shocks and blows that stress the alloy beyond itsyield point but within its breaking strength. It is also a measure ofthe reserve strength of an alloy in a dental structure such as would berequired if the piece were dropped on a tile floor. The toughness factoris defined herein as the product obtained by multiplying the percentageof elongation and the ultimate tensile strength of the alloy in poundsper square inch. Ultimate tensile strength (UTS) is the greatest unitstress an alloy will withstand in tension to the point of breaking.Other physical properties which may be evaluated in describing thealloys embodied herein are as follows: Hardness is the resistance of analloy to surface penetration and is a measure of surface Wear effects.The hardness is determined herein as Diamond Point Hardness (DPH).

Workers in the art of cobalt-chromium denture alloys have believed thatdecreasing the contents of molybdenum and carbon reduces the hardness ofthe alloy while at the same time reducing its strength. It has now beendiscov ered that in the alloy of the present invention, having theaforementioned specifically defined ranges of molybdenum and carbon,hardness is advantageously limited while the strength is excellent. Thisnew alloy has a hardness no greater than about 310 (DPH), an ultimatetensile strength of at least 85,000 p.s.i. and which may reach as highas about 105,000 p.s.i., and a yield strength of at least 50,000 p.s.i.and up to about 60,000 p.s.i. As mentioned previously, the elongation isat least 10%, but in the preferred alloys can range to about 15%; thetoughness factor is at least 9000 and can range up to about 13,000. Thisremarkable toughness feature is demonstrated by the fact that claspattachment elements are highly adjustable, e.g., through an angle offrom about forty to sixty degrees compared to only five to ten degreesof adjustment permitted without breakage for prior known alloys.

In addition to the aforementioned essential elements, other metallic andnon-metallic elements may be incorporated in the alloy, some present asaccidental impurities. Iron content should not exceed 2%; manganesecontent should not exceed 1%; silicon content should not exceed 1%;boron content should not exceed 0.01%; and sulfur content should notexceed 0.02%. Phosphorus contamination should be avoided as this elementcauses hardness and embrittlement.

The chromium content of the alloy should not be materially reduced notincreased beyond the aforementioned ranges. An alloy having a lowchromium content readily corrodes and high chromium causes brittleness.Increased cobalt content produces a harder alloy, whereas increasednickel content produces a softener material. The alloy of thisinvention, however, provides an excellent balance of properties. As isknown in the art, molybdenum and tungsten are substantial equivalents incobalt-chromium alloys, although in the present invention somewhatinferior results are obtained by such a substitution. When a portion ofthe molybdenum requirement of the alloy is replaced by an equivalentamount of tungsten, hardness is increased and castability is reduced;however the toughness value of the alloy, although somewhat reduced, issufiicient for the uses intended.

The examples next set forth illustrate the properties of the claimedalloy and the criticality of the ranges of essential components. Allalloys were made under argon atmosphere using conduction type heatingunits. The alloys were cast by normal dental techniques in ethylsilicate type investments at 1600 F. under argon atmosphereandbench-cooled in the mold. Table I describes compositions wherein theamounts of critical elements, especially molybdenum and carbon, areoutside the essen tial ranges claimed. The physical properties of these'7 alloys, summarized in Table II, show that the alloys fail y g n0777007 p H .560 11M M 000 e Pb E m1 n m m n mmmnmma m mm md m odenwod.1 w H M m 6 0224221 6 h e F LLL w w mo m. m 0. 000 6 a m n r n u ms 0ammm ha a .1 0 .00 e a m e 000 n l 1 cm W mm. s 0 531999 .1 1 md m m. om M Mttaaaa AVU w H m .1 9224585 u 2. a 1 m immun C S 9 E 11 m w m s L ak h B V. 511 335 bk g g A .w m 2 .3772 P3 w m T n O n .S m ned 5% n .1153 W O nhh 5mm y um W e a S d m mm t o u e w 0 n w m m N n m. m m m n n6 r MW m 0 m5 0 7 8901 111.1122 m nm m t ed g E 5 0 1 to meet thedesired criteria in one or more respects, i.e., in suflicient toughness,inadequate yield strength, low elongation and/or undesirable hardness.For instance, the alloys of Examples 9 and 10 contain the claimedamounts of Mo, Ni and Co, but carbon contents are outside the criticalrange; the alloys of Examples 11 and 12 contain the proper amount ofcarbon, Ni and Co, but the Mo content is not in the claimed range. Onthe other hand the alloy of Example 8 that contains the proper amountsof Mo and carbon but the improper amounts of cobalt and nickel showsinferior properties. The alloy of Example 13, a composition as disclosedby E. R. Touceda in Fe Si Mn TABLE I Alloy composition, weight percentCr N1 Mo US. 2,103,500, has a very low and unacceptable yield 15strength. The alloy of Example 14, a composition as described by E. M.Prosen in US. 2,674,571, has poor elongation and toughness.

Example No.:

0000000 wanna? w% m m s a 3 a W ,nm Gd w 00 00 o m a nwmmnmm m c P H BH%%%m mo... 2 2062052 0 40 42 0 a 1 11 11 ok 1 w t a 5 55m68 m an an Mamemdm 051051 mm m M 9 0m 61 c0 8 S 1 Da e o7 oo n 2 V. N I Mm m m v & IMNVh 1 01 C 7 V. 22 mA IM bmfl 0 55550 6fifi8fimmmflflwflm 000000000000000100006 888755374 000 000 000 000 wmmmmmmmmwmm LLLL LO0LOL 0003 5 2225.6A -%fimm m '55 .33 3 32544 3337 .0786 7558 asmmmm 92 2 9. 10117 5 2 n1 11 8717 033603066 2222 20 0 555 5605 zezm zeewwmn 6 0665503 TABLE H atoughness factor of at least 9000, the toughness factor being theproduct obtained by multiplying the percentys p perties age ofelongation and the ultimate tensile strength of said Yield alloy inpounds per square inch.

51 To H ran 5 2. An alloy in accordance with claim 1 wherein thep.s.i.X10 p.s.i. 10 gergni: fang a DPGE cobalt content is to 40 3. Adenture casting made from the alloy of claim 1.

' Example No.:

11 77 3 55 77 u u m n u r N "u e E .n d T n n m e A a uuP sam X. m E d mv. cTwfi Auo m C I .mSTG h m D we. N, min HM we 0 07 ne m m .C 22m 5 4mmmmmmm zg gg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIONPatent No. 3, 544, 315 Dated December L 197 Inventor(s) KamalAsgar' Itis certified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

r- Column 1, line 67, after "zero", insert -load-;

Column 2, line 49, "not", should read nor-;

Column 3, Table II, line 51, 5th column, last number "4, 765" shouldread -4, 675--;

Column 4, Table III, line 15, 7th column, last number "0.1"

should read -l. 0-.

SIGN?) A1 mum 559 1971 oer mm B- BGHUYIAER, Amoffi Oomiiseionar ofPatents

